Fire suppression sprinkler systems comprise a piping network having branches extending throughout a building or other structure through which water or other fire suppressing fluid may be conveyed to be discharged on a fire within the structure. Sprinkler heads are mounted on the piping network and positioned throughout the structure, the sprinkler heads opening in response to a fire event to effect the water discharge. The piping network is connected to a source of pressurized water. Flow of water from the source to the network is controlled by a valve.
One characteristic which may be used to distinguish fire suppression sprinkler systems from one another is whether the system is a “wet” system or a “dry” system. In a wet system, pressurized water is present throughout the piping network when the system is in the ready state. The water is prevented from being discharged by the sprinkler heads themselves, which remain closed unless a fire event is detected. Once a fire occurs, the sprinkler heads in the vicinity of the fire open and immediately discharge water onto the fire. The valve which controls water flow from the source to the sprinkler heads opens in response to the demand for water flow.
In contrast, a compressed gas, typically compressed air, fills the piping network in a dry system when the system is in the ready state. The valve which controls the flow of water to the sprinkler heads is held closed and prevents water from entering the piping network until a fire event is detected. The valve is controlled by a system actuator which is capable of sensing a drop in the air pressure within the piping network occasioned, for example, when a sprinkler head opens in response to a fire event. When the sprinkler head opens, it discharges compressed air from the network, causing the air pressure to drop within the piping network. The system actuator senses the pressure drop and opens the valve, which allows water to flow into the piping network. The water displaces the air in the system and eventually reaches the open sprinkler head, which discharges the water onto the fire. Latched clapper valves are advantageous but high air pressure in conjunction with a low differential clapper design are also feasible.
Wet systems are preferred unless freezing environments are expected. Water is immediately available at the sprinkler heads for discharge as soon as one or more heads opens, thus providing rapid response to suppress a fast spreading fire. Dry systems are used when the piping network is subjected to temperatures that are below the freezing point of the water or other liquid used to suppress the fire. This may occur, for example, in an unheated structure, such as a warehouse located in a temperate zone where the ambient temperature varies seasonally below freezing for extended periods.
The valves used in the wet system to control the flow of water from the source to the network are different from those used in the dry system. Wet system valves act as check valves and open in response to a demand for water flow, but close automatically when demand for flow ceases. In contrast, dry system valves are held closed and are opened by a system actuator that responds to one or more indications of a fire event, for example, loss of air pressure in the piping network. The valve may also be actuated directly by a pressure differential.
It is often desirable to have the option to operate a sprinkler system in either the wet or the dry mode as a particular situation demands. This would be advantageous, for example, in unheated warehouses in cold climates to permit faster water delivery during warm periods. Furthermore, it may also be desired to readily convert a system from the wet to the dry mode or vice versa. This would be advantageous, for example, if the use to which the structure in which the sprinkler system is positioned changes. The prior art practice for effecting such multi-mode systems is to install both a wet system valve and a dry system valve, and all of their appurtenant auxiliary valves and components, in series with one another between the water source and the piping network. Then, depending upon which sprinkler system is desired, the appropriate valves and their associated components and auxiliary valves are used, and the valves associated with the other system are bypassed or otherwise opened or closed as required to isolate them. Using two valves and all of their associated components is complex and expensive however. There is clearly a need for an alternative which allows a sprinkler system to readily be converted from wet to dry mode and back again as required in response to a particular demand.